Why cannot WPS PDF add a note/annotation in Bengali language?

I can add a note or annotation in English language while reading a pdf file in WPS PDF. But when I try to add a note in Bengali language some square boxes appear instead of showing it in Bengali.

Besides, if the title of the pdf file is in Bengali, it also shows some boxes instead of showing the actual Bengali text.

I tried Changing the font (which supports Bengali, e.g. Jamrul) in settings, but it didn't work.

Now, I don't know wheather this problem occurs with other languages. I installed WPS OFFICE from the original deb file downloaded from the official website.

Special Note: I am able to write in Bengali in WPS Writer, LibreOffice Writer and Notepadqq.